The TDs can only be employed within the framework of the current rules. If no technical "catch-all" rule can be used, you face a situation where you need to use the other routes to creating regulation.
I think 7.5 was quite important actually. If nothing else it kept a certain amount of power away from none-independent entities. I suspect that that pleasure is no longer in the hands of the FIA since cars will be regulation-wise faster in 2017, which is against the nature of atleast the "Mosley FIA" and in my opinion, also against the nature of the "Todt FIA", who made the sport slower for the exact same reason in 2014. I even suspect that 7.5 or its 2012 counterpart will have used to set the 2014 aero rules, as well as the exhaust position in 2012 (which although was considered as moveable aero in 2011, I don't really see how one could create a TD in that regard.).